1. Field of the Invention
The present invention relates to catalysts used for hydrocracking, hydrodesulfurization, hydrodenitrogenation, transalkylation, disproportionation, hydrogenation, and alkylation, and particularly to a catalyst exhibiting hydrogen spillover effect to enhance catalytic efficiency.
2. Description of the Related Art
Many organic reactions require the addition of hydrogen, particularly in petroleum refining. Hydrocracking, for example, is a process that is used to produce gasoline, diesel fuel, and jet fuel from aromatic feedstocks. The process requires the addition of hydrogen at high pressure to add hydrogen to aromatic centers, and an acid-catalyzed cracking of paraffinic side chains on the aromatic molecules. In addition, nitrogen and sulfur must be removed from the feedstock to avoid acid-base reactions with the acid catalyst used to crack the paraffinic side chains. This is typically accomplished by hydrodenitrogenation (adding hydrogen to the feedstock before introduction to the cracking reactor) to form ammonia) and hydrodesulfurization (adding hydrogen to the feedstock before introduction to the cracking reactor to form hydrogen sulfide).
Nevertheless, molecular hydrogen is not very reactive. In order to speed the reaction, hydrocracking reactors use a catalyst to break the molecular hydrogen down to atomic hydrogen. The catalyst used to activate the hydrogen is generally a metal, which may be a noble or precious metal, or may be molybdenum, tungsten, nickel, iron, or the like. The catalyst for a hydrocracking reactor is typically an acidic zeolite bed loaded with the metal catalyst.
However, the conventional hydrocracking reactor bed separates the site of activated hydrogen from the acidic cracking sites. It has been noted that some specially constructed beds exhibit an effect known as hydrogen spillover, in which the activated atomic hydrogen spills over into the pores of the support bed. It is thought that this speeds the process of reduction of the aromatic hydrocarbon centers, as well as saturating olefinic side chains. Some catalysts have also been developed to utilize this effect to selectively promote desired reactions, and in the development of hydrogen fuel cells.
Several of the present inventors described a catalyst exhibiting hydrogen spillover effect in an article published in Applied Catalysis A: General, Vol. 277, Issues 1-2, pp. 63-72 in March 2002, which is hereby incorporated by reference. The catalyst described therein generally comprised a smectite clay having rhodium impregnated over the clay by incipient wetness method, which was then ion-exchanged with cobalt nitrate to produce a clay catalyst having 20 wt % CoO and 1 wt % rhodium. The catalyst was compared to a similar catalyst without the noble metal and to a commercial hydrocracking catalyst by a procedure known as Temperature-Programmed Reduction (TPR), which measures the total amount of hydrogen consumed as a function of temperature, and which allows calculation of the degree of reduction and the temperature at which different species are reduced. TPR is a technique sometimes used to measure hydrogenation and hydrogen spillover effects. See “Selective Hydrogenation of Cinnamaldehyde With Pt and Pt—Fe Catalysts: Effects of the Support,” A. B. daSilva et al., Braz. J. Chem. Eng., Vol. 15, No. 2 (1998), pp. 140-144.
Nevertheless, due to the expense of precious or noble metals and the need to moderate temperatures in various organic reactions, such as those taking place during hydrocracking, there is a need to obtain greater efficiency in catalysts exhibiting hydrogen spillover effect.
None of the above publications, taken either singly or in combination, is seen to describe the instant invention as claimed. Thus, a catalyst exhibiting hydrogen spillover effect solving the aforementioned problems is desired.